3GPP has been continuously working on the further evolutions of Long Term Evolution (LTE) to meet the demands for even higher data rates and network capacity. A lot of advanced features have been introduced to enhance the peak data rate, such as Multi-Input Multi-Output (MIMO), Coordinated MultiPoint transmission/reception (COMP), Carrier Aggregation (CA). However, these techniques mainly target to boost the data channel. With the exploding growth in the number of connections per cell, the control channel capacity becomes the bottleneck of the system performance. The design principles of control channel in early releases are not appropriate any more. Currently 3GPP is working on designing a new control channel, termed as “enhanced PDCCH (ePDCCH)” hereunder.
The discussions in RAN1 for ePDCCH is ongoing and a lot of details have not yet been decided, e.g. eREG/eCCE to RE mapping, DM-RS antenna port association and scrambling sequence initialization, search space design, PUCCH HARQ-ACK resource allocation for ePDCCH, etc.
In the ePDCCH discussion, whether to signal the CRS configuration for each ePDCCH set has not been decided in 3GPP. In each ePDCCH set, if the CRS configuration is different from serving cell CRS configuration, how to handle the serving cell CRS and ePDCCH RE mapping is still to be discussed.